How does payment in dorm works

I currently live in a dorm and have a roommate who was absent for three weeks. He asked if it would be okay for him to pay only 15% of the electric bill, and the second roommate and I agreed. However, on the bill's due date, the third roommate divided the amount equally among all four of us, including the absent roommate, and stated that the electric bill should be equally distributed regardless of whether someone is present or not. We never discussed the distribution of the payment for the electric bill when one of the roommates is absent before moving into the dorm.

How should payments in a dorm be handled when one roommate is absent for weeks? Should the bill be equally distributed among all, or should the absent roommate pay less?

Edit: He thinks it’s unfair for him to pay the same amount, considering he was away for almost a month and didn’t consume anything, but he still paid the full rent. So he only paid 15% of the electric bill